WebTransport using HTTP/2
draft-ietf-webtrans-http2-04
The information below is for an old version of the document.
| Document | Type |
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|---|---|---|---|
| Authors | Alan Frindell , Eric Kinnear , Tommy Pauly , Martin Thomson , Victor Vasiliev , Guowu Xie | ||
| Last updated | 2022-09-19 | ||
| Replaces | draft-kinnear-webtransport-http2 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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| Additional resources | Mailing list discussion | ||
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draft-ietf-webtrans-http2-04
webtrans A. Frindell
Internet-Draft Facebook Inc.
Intended status: Standards Track E. Kinnear
Expires: 23 March 2023 T. Pauly
Apple Inc.
M. Thomson
Mozilla
V. Vasiliev
Google
G. Xie
Facebook Inc.
19 September 2022
WebTransport using HTTP/2
draft-ietf-webtrans-http2-04
Abstract
WebTransport defines a set of low-level communications features
designed for client-server interactions that are initiated by Web
clients. This document describes a protocol that can provide many of
the capabilities of WebTransport over HTTP/2. This protocol enables
the use of WebTransport when a UDP-based protocol is not available.
Note to Readers
Discussion of this draft takes place on the WebTransport mailing list
(webtransport@ietf.org (mailto:webtransport@ietf.org)), which is
archived at https://mailarchive.ietf.org/arch/
search/?email_list=webtransport.
The repository tracking the issues for this draft can be found at
https://github.com/ietf-wg-webtrans/draft-webtransport-http2. The
web API draft corresponding to this document can be found at
https://w3c.github.io/webtransport/.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 23 March 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3
3. Session Establishment . . . . . . . . . . . . . . . . . . . . 4
3.1. Establishing a Transport-Capable HTTP/2 Connection . . . 5
3.2. Extended CONNECT in HTTP/2 . . . . . . . . . . . . . . . 5
3.3. Creating a New Session . . . . . . . . . . . . . . . . . 5
3.4. Limiting the Number of Simultaneous Sessions . . . . . . 6
4. WebTransport Features . . . . . . . . . . . . . . . . . . . . 6
4.1. Transport Considerations . . . . . . . . . . . . . . . . 6
4.2. WebTransport Streams . . . . . . . . . . . . . . . . . . 7
5. WebTransport Frames . . . . . . . . . . . . . . . . . . . . . 7
5.1. WT_PADDING Frames . . . . . . . . . . . . . . . . . . . . 8
5.2. WT_RESET_STREAM Frames . . . . . . . . . . . . . . . . . 8
5.3. WT_STOP_SENDING Frames . . . . . . . . . . . . . . . . . 9
5.4. WT_STREAM Frames . . . . . . . . . . . . . . . . . . . . 9
5.5. WT_MAX_DATA Frames . . . . . . . . . . . . . . . . . . . 10
5.6. WT_MAX_STREAM_DATA Frames . . . . . . . . . . . . . . . . 11
5.7. WT_MAX_STREAMS Frames . . . . . . . . . . . . . . . . . . 11
5.8. WT_DATA_BLOCKED Frames . . . . . . . . . . . . . . . . . 12
5.9. WT_STREAM_DATA_BLOCKED Frames . . . . . . . . . . . . . . 12
5.10. WT_STREAMS_BLOCKED Frames . . . . . . . . . . . . . . . . 13
5.11. WT_DATAGRAM Frames . . . . . . . . . . . . . . . . . . . 13
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7. Session Termination . . . . . . . . . . . . . . . . . . . . . 16
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8. Transport Properties . . . . . . . . . . . . . . . . . . . . 16
9. Security Considerations . . . . . . . . . . . . . . . . . . . 17
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
10.1. HTTP/2 SETTINGS Parameter Registration . . . . . . . . . 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . 18
11.2. Informative References . . . . . . . . . . . . . . . . . 19
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 20
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
WebTransport [OVERVIEW] is designed to provide generic communication
capabilities to Web clients that use HTTP/3 [HTTP3]. The HTTP/3
WebTransport protocol [WEBTRANSPORT-H3] allows Web clients to use
QUIC [QUIC] features such as streams or datagrams [DATAGRAM].
However, there are some environments where QUIC cannot be deployed.
This document defines a protocol that provides all of the core
functions of WebTransport using HTTP semantics. This includes
unidirectional streams, bidirectional streams, and datagrams.
By relying only on generic HTTP semantics, this protocol might allow
deployment using any HTTP version. However, this document only
defines negotiation for HTTP/2 [H2] as the current most common TCP-
based fallback to HTTP/3.
1.1. Terminology
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document follows terminology defined in Section 1.2 of
[OVERVIEW]. Note that this document distinguishes between a
WebTransport server and an HTTP/2 server. An HTTP/2 server is the
server that terminates HTTP/2 connections; a WebTransport server is
an application that accepts WebTransport sessions, which can be
accessed using HTTP/2 and this protocol.
2. Protocol Overview
WebTransport servers are identified by an HTTPS URI as defined in
Section 4.2.2 of [HTTP].
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When an HTTP/2 connection is established, both the client and server
have to send a SETTINGS_ENABLE_WEBTRANSPORT setting in order to
indicate that they both support WebTransport over HTTP/2.
A client initiates a WebTransport session by sending an extended
CONNECT request [RFC8441]. If the server accepts the request, a
WebTransport session is established. The stream that carries the
CONNECT request is used to exchange bidirectional data for the
session. This stream will be referred to as a _CONNECT stream_. The
stream ID of a CONNECT stream, which will be referred to as a
_Session ID_, is used to uniquely identify a given WebTransport
session within the connection.
After the session is established, endpoints exchange _WebTransport
frames_ using the bidirectional CONNECT stream. Within this stream,
_WebTransport streams_ and _WebTransport datagrams_ are multiplexed.
In HTTP/2, WebTransport frames are carried in HTTP/2 DATA frames.
Multiple independent WebTransport sessions can share a connection if
the HTTP version supports that, as HTTP/2 does.
WebTransport frames closely mirror a subset of QUIC frames and
provide the essential WebTransport features. Within a WebTransport
session, endpoints can
* create and use bidirectional or unidirectional streams with no
additional round trips using WT_STREAM frames
Stream creation and data flow on streams uses flow control mechanisms
modeled on those in QUIC. Flow control is managed using the
WebTransport frames: WT_MAX_DATA, WT_MAX_STREAM_DATA, WT_MAX_STREAMS,
WT_DATA_BLOCKED, WT_STREAM_DATA_BLOCKED, and WT_STREAMS_BLOCKED.
Flow control for the CONNECT stream as a whole, as provided by the
HTTP version in use, applies in addition to any WebTransport-session-
level flow control.
WebTransport streams can be aborted using a WT_RESET_STREAM frame and
a receiver can request that a sender stop sending with a
WT_STOP_SENDING frame.
A WebTransport session is terminated when the CONNECT stream that
created it is closed. This implicitly closes all WebTransport
streams that were multiplexed over that CONNECT stream.
3. Session Establishment
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3.1. Establishing a Transport-Capable HTTP/2 Connection
In order to indicate support for WebTransport, both the client and
the server MUST send a SETTINGS_ENABLE_WEBTRANSPORT value set to "1"
in their SETTINGS frame. Endpoints MUST NOT use any WebTransport-
related functionality unless the parameter has been negotiated.
3.2. Extended CONNECT in HTTP/2
[RFC8441] defines an extended CONNECT method in Section 4, enabled by
the SETTINGS_ENABLE_CONNECT_PROTOCOL parameter. An endpoint does not
need to send both SETTINGS_ENABLE_CONNECT_PROTOCOL and
SETTINGS_ENABLE_WEBTRANSPORT; the SETTINGS_ENABLE_WEBTRANSPORT
setting implies that an endpoint supports extended CONNECT.
3.3. Creating a New Session
As WebTransport sessions are established over HTTP, they are
identified using the https URI scheme [RFC7230].
In order to create a new WebTransport session, a client can send an
HTTP CONNECT request. The :protocol pseudo-header field ([RFC8441])
MUST be set to webtransport (Section 7.1 of [WEBTRANSPORT-H3]). The
:scheme field MUST be https. Both the :authority and the :path value
MUST be set; those fields indicate the desired WebTransport server.
In a Web context, the request MUST include an Origin header field
[ORIGIN] that includes the origin of the site that requested the
creation of the session.
Upon receiving an extended CONNECT request with a :protocol field set
to webtransport, the HTTP server checks if the identified resource
supports WebTransport sessions. If the resource does not, the server
SHOULD reply with status code 404 (Section 6.5.4 of [RFC7231]). To
accept a WebTransport session the server replies with 2xx status
code. Before accepting a session, a server MUST ensure that it
authorizes use of the session by the site identified in the Origin
header.
From the client's perspective, a WebTransport session is established
when the client receives a 200 response. From the server's
perspective, a session is established once it sends a 200 response.
Both endpoints MUST NOT send any WebTransport frames on a given
session before that session is established.
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3.4. Limiting the Number of Simultaneous Sessions
From a flow control perspective, WebTransport sessions count against
HTTP/2 session flow control limits just like regular HTTP requests,
since they are established via an HTTP CONNECT request. This
document does not make any effort to introduce a separate flow
control mechanism for WebTransport sessions. If the server needs to
limit the rate of incoming requests, it has alternative mechanisms at
its disposal:
* HTTP_STREAM_REFUSED error code defined in [RFC7540] indicates to
the receiving HTTP/2 stack that the request was not processed in
any way.
* HTTP status code 429 indicates that the request was rejected due
to rate limiting [RFC6585]. Unlike the previous method, this
signal is directly propagated to the application.
4. WebTransport Features
WebTransport over TCP-based HTTP semantics provides the following
features described in [OVERVIEW]: unidirectional streams,
bidirectional streams, and datagrams, initiated by either endpoint.
WebTransport streams and datagrams that belong to different
WebTransport sessions are identified by the CONNECT stream on which
they are transmitted, with one WebTransport session consuming one
CONNECT stream.
4.1. Transport Considerations
Because WebTransport over TCP-based HTTP semantics relies on the
underlying protocols to provide in order and reliable delivery, there
are some notable differences from the way in which QUIC handles
application data.
Endpoints MUST send stream data in order. As there is no ordering
mechanism available for the receiver to reassemble incoming data,
receivers assume that all data arriving in STREAM frames is
contiguous and in order.
DATAGRAM frames are delivered to the remote WebTransport endpoint
reliably, however this does not require that the receiving
implementation deliver that data to the application in a reliable
manner.
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4.2. WebTransport Streams
WebTransport streams have identifiers and states that mirror the
identifiers ((Section 2.1 of [RFC9000])) and states (Section 3 of
[RFC9000]) of QUIC streams as closely as possible to aid in ease of
implementation.
WebTransport streams are identified by a numeric value, or stream ID.
Stream IDs are only meaningful within the WebTransport session in
which they were created. They share the same semantics as QUIC
stream IDs, with client initiated streams having even-numbered stream
IDs and server-initiated streams having odd-numbered stream IDs.
Similarly, they can be bidirectional or unidirectional, indicated by
the second least significant bit of the stream ID.
Because WebTransport does not provide an acknowledgement mechanism
for WebTransport frames, it relies on the underlying transport's in
order delivery to inform stream state transitions. Wherever QUIC
relies on receiving an ack for a packet to transition between stream
states, WebTransport performs that transition immediately.
5. WebTransport Frames
WebTransport frames mirror their QUIC counterparts as closely as
possible to enable maximal reuse of any applicable QUIC
infrastructure by implementors.
A WebTransport frame begins with a Frame Type and Frame Length which
are followed by zero or more fields that are type-dependent.
Frame {
Frame Type (i),
Frame Length (i),
Type-Dependent Fields (..),
}
Figure 1: WebTransport Frame Format
The Frame Type field indicates the type of the frame, defining what
type-dependent fields will be present.
The Frame Length field indicates the length of the WebTransport
frame, including all type-dependent fields and other information. It
does not include the size of the Frame Type or Frame Length fields
themselves.
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Both of these fields use a variable-length integer encoding (see
Section 16 of [RFC9000]), with one exception. To ensure simple and
efficient implementations of frame parsing, the frame type and length
MUST use the shortest possible encoding. For example, for the frame
types defined in this document, this means a single-byte encoding,
even though it is possible to encode these values as a two-, four-,
or eight-byte variable-length integer.
5.1. WT_PADDING Frames
A WT_PADDING frame (type=0x00) has no semantic value. PADDING frames
can be used to introduce additional data between other WebTransport
frames and can also be used to provide protection against traffic
analysis or for other reasons.
WT_PADDING Frame {
Type (i) = 0x00,
Length (i),
Padding (..),
}
Figure 2: WT_PADDING Frame Format
The Padding field MUST be set to an all-zero sequence of bytes of any
length as specified by the Length field.
5.2. WT_RESET_STREAM Frames
A WebTransport frame called WT_RESET_STREAM is introduced for either
endpoint to abruptly terminate the sending part of a WebTransport
stream.
An endpoint uses a WT_RESET_STREAM frame (type=0x04) to abruptly
terminate the sending part of a stream.
After sending a WT_RESET_STREAM, an endpoint ceases transmission of
WT_STREAM frames on the identified stream. A receiver of
WT_RESET_STREAM can discard any data that it already received on that
stream.
WT_RESET_STREAM Frame {
Type (i) = 0x04,
Length (i),
Stream ID (i),
Application Protocol Error Code (i),
}
Figure 3: WT_RESET_STREAM Frame Format
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The WT_RESET_STREAM frame defines the following fields:
Stream ID: A variable-length integer encoding of the WebTransport
stream ID of the stream being terminated.
Application Protocol Error Code: A variable-length integer
containing the application protocol error code that indicates why
the stream is being closed.
Unlike the equivalent QUIC frame, this frame does not include a Final
Size field. In-order delivery of WT_STREAM frames ensures that the
amount of session-level flow control consumed by a stream is always
known by both endpoints.
5.3. WT_STOP_SENDING Frames
A WebTransport frame called WT_STOP_SENDING is introduced to
communicate that incoming data is being discarded on receipt per
application request. WT_STOP_SENDING requests that a peer cease
transmission on a stream.
WT_STOP_SENDING Frame {
Type (i) = 0x05,
Length (i),
Stream ID (i),
Application Protocol Error Code (i),
}
Figure 4: WT_STOP_SENDING Frame Format
The WT_STOP_SENDING frame defines the following fields:
Stream ID: A variable-length integer carrying the WebTransport
stream ID of the stream being ignored.
Application Protocol Error Code: A variable-length integer
containing the application-specified reason the sender is ignoring
the stream.
5.4. WT_STREAM Frames
WT_STREAM frames implicitly create a stream and carry stream data.
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The Type field in the WT_STREAM frame is either 0x0a or 0x0b. This
uses the same frame types as a QUIC STREAM frame with the OFF bit
clear and the LEN bit set. The FIN bit (0x01) in the frame type
indicates that the frame marks the end of the stream in one
direction. Stream data consists of any number of 0x0a frames
followed by a terminal 0x0b frame.
WT_STREAM Frame {
Type (i) = 0x0a..0x0b,
Length (i),
Stream ID (i),
Stream Data (..),
}
Figure 5: WT_STREAM Frame Format
WT_STREAM frames contain the following fields:
Stream ID: The stream ID for the stream.
Stream Data: Zero or more bytes of data for the stream. Empty
WT_STREAM frames MUST NOT be used unless they open or close a
stream; an endpoint MAY treat an empty WT_STREAM frame that
neither starts nor ends a stream as a session error.
5.5. WT_MAX_DATA Frames
A WebTransport frame called WT_MAX_DATA is introduced to inform the
peer of the maximum amount of data that can be sent on the
WebTransport session as a whole.
WT_MAX_DATA Frame {
Type (i) = 0x10,
Length (i),
Maximum Data (i),
}
Figure 6: WT_MAX_DATA Frame Format
WT_MAX_DATA frames contain the following field:
Maximum Data: A variable-length integer indicating the maximum
amount of data that can be sent on the entire connection, in units
of bytes.
All data sent in WT_STREAM frames counts toward this limit. The sum
of the lengths of Stream Data fields in WT_STREAM frames MUST NOT
exceed the value advertised by a receiver.
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5.6. WT_MAX_STREAM_DATA Frames
A WebTransport frame called WT_MAX_STREAM_DATA is introduced to
inform a peer of the maximum amount of data that can be sent on a
stream.
WT_MAX_STREAM_DATA Frame {
Type (i) = 0x11,
Length (i),
Stream ID (i),
Maximum Stream Data (i),
}
Figure 7: WT_MAX_STREAM_DATA Frame Format
WT_MAX_STREAM_DATA frames contain the following fields:
Stream ID: The stream ID of the affected WebTransport stream,
encoded as a variable-length integer.
Maximum Stream Data: A variable-length integer indicating the
maximum amount of data that can be sent on the identified stream,
in units of bytes.
All data sent in WT_STREAM frames for the identified stream counts
toward this limit. The sum of the lengths of Stream Data fields in
WT_STREAM frames on the identified stream MUST NOT exceed the value
advertised by a receiver.
5.7. WT_MAX_STREAMS Frames
A WebTransport frame called WT_MAX_STREAMS is introduced to inform
the peer of the cumulative number of streams of a given type it is
permitted to open. A WT_MAX_STREAMS frame with a type of 0x12
applies to bidirectional streams, and a WT_MAX_STREAMS frame with a
type of 0x13 applies to unidirectional streams.
WT_MAX_STREAMS Frame {
Type (i) = 0x12..0x13,
Length (i),
Maximum Streams (i),
}
Figure 8: WT_MAX_STREAMS Frame Format
WT_MAX_STREAMS frames contain the following field:
Maximum Streams: A count of the cumulative number of streams of the
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corresponding type that can be opened over the lifetime of the
connection. This value cannot exceed 2^60, as it is not possible
to encode stream IDs larger than 2^62-1.
An endpoint MUST NOT open more streams than permitted by the current
stream limit set by its peer. For instance, a server that receives a
unidirectional stream limit of 3 is permitted to open streams 3, 7,
and 11, but not stream 15.
Note that this limit includes streams that have been closed as well
as those that are open.
5.8. WT_DATA_BLOCKED Frames
A sender SHOULD send a WT_DATA_BLOCKED frame (type=0x14) when it
wishes to send data but is unable to do so due to WebTransport
session-level flow control. WT_DATA_BLOCKED frames can be used as
input to tuning of flow control algorithms.
WT_DATA_BLOCKED Frame {
Type (i) = 0x14,
Length (i),
Maximum Data (i),
}
Figure 9: WT_DATA_BLOCKED Frame Format
WT_DATA_BLOCKED frames contain the following field:
Maximum Data: A variable-length integer indicating the session-level
limit at which blocking occurred.
5.9. WT_STREAM_DATA_BLOCKED Frames
A sender SHOULD send a WT_STREAM_DATA_BLOCKED frame (type=0x15) when
it wishes to send data but is unable to do so due to stream-level
flow control. This frame is analogous to WT_DATA_BLOCKED.
WT_STREAM_DATA_BLOCKED Frame {
Type (i) = 0x15,
Length (i),
Stream ID (i),
Maximum Stream Data (i),
}
Figure 10: WT_STREAM_DATA_BLOCKED Frame Format
WT_STREAM_DATA_BLOCKED frames contain the following fields:
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Stream ID: A variable-length integer indicating the WebTransport
stream that is blocked due to flow control.
Maximum Stream Data: A variable-length integer indicating the offset
of the stream at which the blocking occurred.
5.10. WT_STREAMS_BLOCKED Frames
A sender SHOULD send a WT_STREAMS_BLOCKED frame (type=0x16 or 0x17)
when it wishes to open a stream but is unable to do so due to the
maximum stream limit set by its peer. A WT_STREAMS_BLOCKED frame of
type 0x16 is used to indicate reaching the bidirectional stream
limit, and a STREAMS_BLOCKED frame of type 0x17 is used to indicate
reaching the unidirectional stream limit.
A WT_STREAMS_BLOCKED frame does not open the stream, but informs the
peer that a new stream was needed and the stream limit prevented the
creation of the stream.
WT_STREAMS_BLOCKED Frame {
Type (i) = 0x16..0x17,
Length (i),
Maximum Streams (i),
}
Figure 11: WT_STREAMS_BLOCKED Frame Format
WT_STREAMS_BLOCKED frames contain the following field:
Maximum Streams: A variable-length integer indicating the maximum
number of streams allowed at the time the frame was sent. This
value cannot exceed 2^60, as it is not possible to encode stream
IDs larger than 2^62-1.
5.11. WT_DATAGRAM Frames
The WT_DATAGRAM frame type (0x31) is used to carry datagram traffic.
Frame type 0x30 is also reserved to maintain parity with QUIC, but
unused, as all WebTransport frames MUST contain a length field.
WT_DATAGRAM Frame {
Type (i) = 0x31,
Length (i),
Datagram Data (..),
}
Figure 12: WT_DATAGRAM Frame Format
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WT_DATAGRAM frames contain the following fields:
Datagram Data: The content of the datagram to be delivered.
The data in WT_DATAGRAM frames is not subject to flow control. The
receiver MAY discard this data if it does not have sufficient space
to buffer it.
An intermediary could forward the data in a WT_DATAGRAM frame over
another protocol, such as WebTransport over HTTP/3. In QUIC, a
datagram frame can span at most one packet. Because of that, the
applications have to know the maximum size of the datagram they can
send. However, when proxying the datagrams, the hop-by-hop MTUs can
vary.
6. Examples
An example of negotiating a WebTransport Stream on an HTTP/2
connection follows. This example is intended to closely follow the
example in Section 5.1 of [RFC8441] to help illustrate the
differences defined in this document.
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[[ From Client ]] [[ From Server ]]
SETTINGS
SETTINGS_ENABLE_WEBTRANSPORT = 1
SETTINGS
SETTINGS_ENABLE_WEBTRANSPORT = 1
HEADERS + END_HEADERS
Stream ID = 3
:method = CONNECT
:protocol = webtransport
:scheme = https
:path = /
:authority = server.example.com
origin: server.example.com
HEADERS + END_HEADERS
Stream ID = 3
:status = 200
WT_STREAM
Stream ID = 5
WebTransport Data
WT_STREAM + FIN
Stream ID = 5
WebTransport Data
WT_STREAM + FIN
Stream ID = 5
WebTransport Data
An example of the server initiating a WebTransport Stream follows.
The only difference here is the endpoint that sends the first
WT_STREAM frame.
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[[ From Client ]] [[ From Server ]]
SETTINGS
SETTINGS_ENABLE_WEBTRANSPORT = 1
SETTINGS
SETTINGS_ENABLE_WEBTRANSPORT = 1
HEADERS + END_HEADERS
Stream ID = 3
:method = CONNECT
:protocol = webtransport
:scheme = https
:path = /
:authority = server.example.com
origin: server.example.com
HEADERS + END_HEADERS
Stream ID = 3
:status = 200
WT_STREAM
Stream ID = 2
WebTransport Data
WT_STREAM + FIN
Stream ID = 2
WebTransport Data
WT_STREAM + FIN
Stream ID = 2
WebTransport Data
7. Session Termination
An WebTransport session over HTTP/2 is terminated when either
endpoint closes the stream associated with the CONNECT request that
initiated the session. Upon learning about the session being
terminated, the endpoint MUST stop sending new datagrams and reset
all of the streams associated with the session.
8. Transport Properties
The WebTransport framework [OVERVIEW] defines a set of optional
transport properties that clients can use to determine the presence
of features which might allow additional optimizations beyond the
common set of properties available via all WebTransport protocols.
Below are details about support in Http2Transport for those
properties.
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Stream Independence: Http2Transport does not support stream
independence, as HTTP/2 inherently has head of line blocking.
Partial Reliability: Http2Transport does not support partial
reliability, as HTTP/2 retransmits any lost data. This means that
any datagrams sent via Http2Transport will be retransmitted
regardless of the preference of the application. The receiver is
permitted to drop them, however, if it is unable to buffer them.
Pooling Support: Http2Transport supports pooling, as multiple
transports using Http2Transport may share the same underlying
HTTP/2 connection and therefore share a congestion controller and
other transport context.
Connection Mobility: Http2Transport does not support connection
mobility, unless an underlying transport protocol that supports
multipath or migration, such as MPTCP [MPTCP], is used underneath
HTTP/2 and TLS. Without such support, Http2Transport connections
cannot survive network transitions.
9. Security Considerations
WebTransport over HTTP/2 satisfies all of the security requirements
imposed by [OVERVIEW] on WebTransport protocols, thus providing a
secure framework for client-server communication in cases when the
client is potentially untrusted.
WebTransport over HTTP/2 requires explicit opt-in through the use of
HTTP SETTINGS; this avoids potential protocol confusion attacks by
ensuring the HTTP/2 server explicitly supports it. It also requires
the use of the Origin header, providing the server with the ability
to deny access to Web-based clients that do not originate from a
trusted origin.
Just like HTTP traffic going over HTTP/2, WebTransport pools traffic
to different origins within a single connection. Different origins
imply different trust domains, meaning that the implementations have
to treat each transport as potentially hostile towards others on the
same connection. One potential attack is a resource exhaustion
attack: since all of the transports share both congestion control and
flow control context, a single client aggressively using up those
resources can cause other transports to stall. The user agent thus
SHOULD implement a fairness scheme that ensures that each transport
within connection gets a reasonable share of controlled resources;
this applies both to sending data and to opening new streams.
10. IANA Considerations
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10.1. HTTP/2 SETTINGS Parameter Registration
The following entry is added to the "HTTP/2 Settings" registry
established by [RFC7540]:
The SETTINGS_ENABLE_WEBTRANSPORT parameter indicates that the
specified HTTP/2 connection is WebTransport-capable.
Setting Name: ENABLE_WEBTRANSPORT
Value: 0x2b603742
Default: 0
Specification: This document
11. References
11.1. Normative References
[H2] Thomson, M. and C. Benfield, "HTTP/2", Work in Progress,
Internet-Draft, draft-ietf-httpbis-http2bis-07, 24 January
2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
httpbis-http2bis-07>.
[HTTP] Fielding, R. T., Nottingham, M., and J. Reschke, "HTTP
Semantics", Work in Progress, Internet-Draft, draft-ietf-
httpbis-semantics-19, 12 September 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-
semantics-19>.
[ORIGIN] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011,
<https://www.rfc-editor.org/rfc/rfc6454>.
[OVERVIEW] Vasiliev, V., "The WebTransport Protocol Framework", Work
in Progress, Internet-Draft, draft-ietf-webtrans-overview-
04, 11 July 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-webtrans-overview-04>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status
Codes", RFC 6585, DOI 10.17487/RFC6585, April 2012,
<https://www.rfc-editor.org/rfc/rfc6585>.
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[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/rfc/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/rfc/rfc7231>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/rfc/rfc7540>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8441] McManus, P., "Bootstrapping WebSockets with HTTP/2",
RFC 8441, DOI 10.17487/RFC8441, September 2018,
<https://www.rfc-editor.org/rfc/rfc8441>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
[WEBTRANSPORT-H3]
Frindell, A., Kinnear, E., and V. Vasiliev, "WebTransport
over HTTP/3", Work in Progress, Internet-Draft, draft-
ietf-webtrans-http3-03, 6 July 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-
webtrans-http3-03>.
11.2. Informative References
[DATAGRAM] Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", Work in Progress, Internet-
Draft, draft-ietf-quic-datagram-10, 4 February 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
datagram-10>.
[HTTP3] Bishop, M., "HTTP/3", Work in Progress, Internet-Draft,
draft-ietf-quic-http-34, 2 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-quic-
http-34>.
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[MPTCP] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
<https://www.rfc-editor.org/rfc/rfc6824>.
[QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
Acknowledgments
Thanks to Anthony Chivetta, Joshua Otto, and Valentin Pistol for
their contributions in the design and implementation of this work.
Index
W
W
WT_DATA_BLOCKED Section 2, Paragraph 7; Section 5.8, Paragraph
1; Section 5.8, Paragraph 1; Section 5.8, Paragraph 3;
Section 5.9, Paragraph 1
WT_DATAGRAM Section 5.11, Paragraph 1; Section 5.11, Paragraph
3; Section 5.11, Paragraph 5; Section 5.11, Paragraph 6
WT_MAX_DATA Section 2, Paragraph 7; Section 5.5, Paragraph 1;
Section 5.5, Paragraph 3
WT_MAX_STREAM_DATA Section 2, Paragraph 7; Section 5.6,
Paragraph 1; Section 5.6, Paragraph 3
WT_MAX_STREAMS Section 2, Paragraph 7; Section 5.7, Paragraph
1; Section 5.7, Paragraph 1; Section 5.7, Paragraph 1;
Section 5.7, Paragraph 3
WT_PADDING Section 5.1, Paragraph 1
WT_RESET_STREAM Section 2, Paragraph 8; Section 5.2, Paragraph
1; Section 5.2, Paragraph 2; Section 5.2, Paragraph 3;
Section 5.2, Paragraph 3; Section 5.2, Paragraph 5
WT_STOP_SENDING Section 2, Paragraph 8; Section 5.3, Paragraph
1; Section 5.3, Paragraph 1; Section 5.3, Paragraph 3
WT_STREAM Section 2, Paragraph 6, Item 1; Section 5.2,
Paragraph 3; Section 5.2, Paragraph 7; Section 5.4,
Paragraph 1; Section 5.4, Paragraph 2; Section 5.4,
Paragraph 4; Section 5.4, Paragraph 5.4.1; Section 5.4,
Paragraph 5.4.1; Section 5.5, Paragraph 5; Section 5.5,
Paragraph 5; Section 5.6, Paragraph 5; Section 5.6,
Paragraph 5; Section 6, Paragraph 3
WT_STREAM_DATA_BLOCKED Section 2, Paragraph 7; Section 5.9,
Paragraph 1; Section 5.9, Paragraph 3
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WT_STREAMS_BLOCKED Section 2, Paragraph 7; Section 5.10,
Paragraph 1; Section 5.10, Paragraph 1; Section 5.10,
Paragraph 2; Section 5.10, Paragraph 4
Authors' Addresses
Alan Frindell
Facebook Inc.
Email: afrind@fb.com
Eric Kinnear
Apple Inc.
One Apple Park Way
Cupertino, California 95014,
United States of America
Email: ekinnear@apple.com
Tommy Pauly
Apple Inc.
One Apple Park Way
Cupertino, California 95014,
United States of America
Email: tpauly@apple.com
Martin Thomson
Mozilla
Email: mt@lowentropy.net
Victor Vasiliev
Google
Email: vasilvv@google.com
Guowu Xie
Facebook Inc.
Email: woo@fb.com
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